1. Technical Field
The present invention relates to an ink composition capable of obtaining a high quality recording matter even on various recording media, particularly non- or low absorbable recording media such as synthetic paper or printing paper.
2. Related Art
An ink jet recording method is a printing method for printing by letting ink droplets fly and attach to a recording medium such as paper. According to recent innovative progress in ink jet recording technology, the ink jet recording method has been also used in the field of highly fine printing that was achieved by silver halide photography or offset printing before. With this, an ink for ink jet recording has been developed so that an image having glossiness similar to that achieved by silver halide photography can be formed by the ink jet recording on so-called exclusive paper, which is a recording medium having high gloss being equal to that of photographic paper or art paper used in the fields of silver halide photography and offset printing. In addition, ink for ink jet recording that can achieve an image quality, even on plain paper, similar to that achieved by silver halide photography has been developed.
Incidentally, desk top publishing (DTP) has been spreading in recent years, in particular, in the printing field, with technology for forming an image from digital data becoming widespread. Even when printing is carried out by DTP, a proof for color proofing is preliminarily prepared in order to confirm the glossiness and color impression of the actual printed matter. The ink jet recording system is applied to the output of the proof, and exclusive paper for ink jet recording is usually used as the recording medium since high color reproducibility and high color stability of the printed matter are required in DTP.
A proof sheet, which is exclusive paper for ink jet recording, is produced so as to exhibit glossiness and color impression similar to those of the actual output printed on printing paper. Thus, the material of the exclusive paper is properly adjusted depending on the type of printing paper. However, production of exclusive paper that can respond to all of the various types of printing paper causes an increase in manufacturing cost. Accordingly, in application to color proofing, it is desired, from the technical viewpoint, to conduct ink jet recording on printing paper rather than on exclusive paper. Furthermore, if it is possible to conduct ink jet recording directly on printing paper, not on exclusive paper, for providing a final proof sample, this can significantly decrease the cost for proof and therefore is desired from the economical viewpoint. In addition, synthetic paper prepared by mixing an inorganic filler and the like with a polyethylene resin, a polypropylene resin or a polyester resin and then forming the mixture into a film is widely used in the printing field. The synthetic paper is excellent in recyclability and thereby has recently received widespread attention as an environment-friendly material. It is desired to record on such synthetic paper, from the environmental viewpoint.
The printing paper is coated paper having a coating layer on the surface for receiving oil-based ink and has a characteristic that the coating layer is poor in ink-absorbing ability against aqueous ink. Therefore, in the use of aqueous pigment ink, which is usually used in ink jet recording, bleeding or beading unevenness may occur in an image because of low permeability of the ink into the recording medium (printing paper).
In view of the above-mentioned problems, for example, JP-A-2005-194500 discloses a pigment ink that is decreased in bleeding and also is excellent in gloss with exclusive paper by including a polysiloxane compound as a surfactant and an alkanediol, such as 1,2-hexanediol, as a solubilization aid. In addition, JP-A-2003-213179, JP-A-2003-253167, or JP-A-2006-249429 proposes that permeability of ink into a recording medium is controlled by adding a diol such as glycerin or 1,3-butanediol or a triol alcohol solvent such as pentanetriol to the ink for forming a high-quality image. However, an ink composition for forming a yet further high-quality image has been demanded up to now.
The inventors have recently found out the fact that when an ink composition contains a slightly water-soluble alkanediol having 7 to 10 carbon atoms and cyclodextrin compound, a high-quality image free from bleeding or beading can be formed even in a case of various recording media, in particular, a non- or low absorbable recording medium such as synthetic paper and printing paper, and is excellent in storage stability of ink. The invention is based on this finding.